U.S. Pat. No. 3,769,463, which issued Oct. 30, 1973, to Philip G. Graham et al. and is entitled "Electronic Long-Distance Telephone Call Computer and Recorder", shows a system for automatically computing and recording the cost of a long distance telephone call which is not fully automated and requires that the user set both the initial and overtime rate for the call in two separate registers. Thus, it is necessary for the user to know both the initial and overtime rate for every call he is to make and manually set the same into the unit in order for the Graham et al. unit to record and display the cost of the call. The Graham device is not suitable as a consumer device since the amount and format of information to be set into the unit is beyond that which the normal consumer would be willing to do for a device of this nature.
U.S. Pat. No. 3,970,793, which issued July 20, 1976, to Leslie M. Profitt et al. and is entitled "Telephone Call Toll Monitor and Indicator", again attempts to provide a unit for monitoring telephone calls. The Profitt device can be used only for long distance calls. This is true because Profitt uses a mechanical clutch for setting telephone rates. This clutch is not suitable for calculating rates in certain areas of the country where message unit areas and intrastate rates apply.
The above devices are attempts at solving the problem of providing a unit for automatically displaying to the user of a telephone the cost of the call while it is in process. Such units have not been developed which are fully automated for several reasons. First, the rate structure around the country varies in a non-linear fashion both for initial charges and for overtime rates. Basically, there are three types of telephone calls, i.e. local calls, intrastate calls, and interstate calls. In many metropolitan areas, the local calls are divided into a maximum of seven message unit areas. Normally, these local rate structures are only in effect in the large metropolitan areas such as New York. The method of billing varies from metropolitan area to metropolitan area and within the various message unit areas. For example, it may be that in a first zone there is no charge for calls (i.e. unlimited calling) and in a second zone there may be a fixed charge for each call while in further zones there may be an initial charge and an incremental charge based upon different time intervals and different rates per unit time depending upon distance.
The telephone rates also vary depending upon whether or not a call is made in the day, evening, or night.
Therefore, it is an object of this invention to provide a new and useful device for indicating the rates of a telephone call.
It is another object of this invention to provide a device which indicates the imminent increase in the accrued cost of a telephone call to allow the user to end the call before the increased cost is incurred.
It is a further object of this invention to provide an apparatus for calculating and displaying the accrued cost of a telephone call in which simple controls operate the same.
It is still a further object of this invention to provide an apparatus for calculating and displaying the accrued cost of a telephone call in which message unit areas, intrastate areas, and interstate areas can be accommodated with the setting of a single slide device.